The objective of this proposal is to improve the detection and characterization of various malignant melanoma lesions using non-invasive gamma camera imaging by developing new ligands labeled with I-123, I-131, Tc-99m and F-18. The desired tracers should produce a high tumor to background ratio at an early time interval after injection. The specific aims are to synthesize a variety of novel and known benzamide derivatives that have been shown by us and others to localize in malignant melanoma. Our recent in vitro competition binding studies have shown that some benzamides bind to melanoma cell surface sigma-1 receptors. In order to obtain optimal derivative (high in vitro affinity for sigma-1 sites and a high in vivo tumor uptake and retention), new benzamide analogs of N- diethylaminoethyl) -4-iodobenzamide and N-(piperidinylaminoethyl)-4- iodobenzamide will be synthesized and assessed for sigma-1 affinity on melanoma cells. The new ligands will be completely characterized by the spectroscopic (NMR, IR, mass spectroscopy) and analytical (HPLC, elemental analysis) methods. To achieve high radiochemical yields and high specific activity in radioiodinations, the tri-n-butyltin derivatives will be synthesized starting from the bromo or iodobenzamide precursor by palladium catalyzed stannylation reaction using bis(tributyltin). Labeling with I-123, I-125 or I-131 will be performed using chloramine-T, peracetic acid, iodogen beads or other oxidizing agents to produce high yields of radiolabeled iodobenzamides in high radiochemical purity. The radiolabeled compounds will be purified using HPLC methods and characterized by the comparison of the retention time of the cold iodobenzamide under identical condition. By synthesizing a number of structurally-related compounds and studying their pharmacologic profiles we will gain a better understanding of the structure-activity relationships of this class of compounds. The iodobenzamide derivatives showing a high specific binding (low Kd) and a low non-specific binding in vitro will be tested further for in-vivo evaluation. The biodistribution of the labeled compounds will be evaluated in nude mice bearing human malignant melanoma. The specificity of binding in vivo will be studied using blocking studies. Various benzamides containing primary amino group will be coupled to bifunctional thiolactone and labeled with Tc-99m and evaluated. Our preliminary results for the evaluation of iodobenzamides in nude mice bearing human malignant melanoma have been very encouraging. Imaging will be performed using nude mice xenografted with human malignant melanoma.